Such a single mode optical fiber is known per se from U.S. Pat. No. 5,905,838, wherein in particular FIG. 4 schematically shows the normalized refractive index difference as a function of radial position for the four region fiber. Thus, the silica core doped with germanium is surrounded by an annular region of depressed index, in this instance, composed of fluorine-doped silica. Surrounding the region is a germano-silica ring, in turn within an outer cladding region of, for example, undoped silica. The core region shows a depressed-index dip characteristic of MCVD produced fiber. Such a fiber is also defined as a so-called “double window WDM (“wavelength division multiplexed”) fiber,” which fiber is used in so-called metro networks or long-distance networks. Such networks are characterized by medium-length transmission distances of up to a few hundred kilometers and a large number of nodes, where branches and/or connections to other (parts of) networks are present. The optical fibers via which the transmission of signals takes place in such networks are preferably suitable for high transmission rates at a large number of different wavelengths.
The article “Maximum effective area for non-zero dispersion-shifted fibre,” discloses refractive index profiles in which a fiber of this type has a dispersion slope of 0.08 ps/(nm2·km) at 1550 nm. The effective area at 1550 nm is in the 45-110 μm2 range. Further details with regard to the slope for obtaining a satisfactory equilibrium of characteristics, in particular as regards the dispersion slope, macro bending and effective area, are not known therefrom.
U.S. Pat. No. 6,396,987 relates to an optical fiber for use in WDM transmission systems, wherein the effective area is larger than or equal to 60 μm2 and the dispersion value ranges from 6 to 10 ps/(nm·km).
European patent application No. 0249230, relates to a method for manufacturing a preform. Since said document only relates to preforms, no specific details are provided with regard to the optical fiber drawn from such a preform, such as the value of the dispersion slope, the dispersion value or the effective area.
European patent application No. 0775924, relates to a single mode optical fiber having a three-segment index profile. Although the zero dispersion wavelength is in the 1520-1600 nm range, the total dispersion slope may be ≦0.095 ps/(nm2·km). No details are provided with regard to the slope required for obtaining a satisfactory equilibrium of characteristics as regards the dispersion slope, macro bending and effective area.
In the case of very long distances (distances of 1000 km and longer) optical fibers for high transmission rates are optimized for use in wavelength range around 1550 nm, in which wavelength range the optical attenuation may be considered low (about 0.2 dB/km). The NZDF (“non-zero dispersion fibers”) also have shifted dispersion, as a result of which the dispersion at a wavelength of 1550 nm is lower than that of a standard single mode fiber. The dispersion value deviates sufficiently from zero, however, for minimizing the effect of non-linear characteristics that may have a seriously adverse effect on the allowable maximum transmission capacity.
Because of the relatively short distances in the aforesaid networks, less strict requirements are made of the optical attenuation, as a result of which also the wavelength range around 1300 nm, which has a characteristic attenuation of about 0.3 dB/km, is in principle suitable for such applications. As a result of the optimization thereof in the 1550 nm wavelength range, the fibers used for long-distance transmission are less suitable for use in the wavelength range around 1300 nm, however.